When installing the KeystoneJS project they use MongoDB as a dependency. I get this following error:

trout@Development:~/keystone4$

js-bson: Failed to load c++ bson extension, using pure JS version

I found a reference to this Stack Overflow discussion:
http://stackoverflow.com/questions/28651028/cannot-find-module-build-release-bson-code-module-not-found-js-bson

To fix the issue:
cd ~/keystone4/node_modules/mongodb/node_modules/bson/ext/
nano index.js

change this line:
bson = require('../build/Release/bson');
to this line:
bson = require('../browser_build/bson');